It is common in the medical sector, in racing sports and in the window/security film industry to deploy single layers of film to reduce the potential for damage or obstruction to clear sight. In many cases, it is advantageous to be able to simply remove and replace dirty or scratched lenses or window films. However, there are cases where one is not in a work environment that allows the time required for such removal and replacement, such as an operating room or driving a motorcycle. This creates a problem. Either one continues with occluded vision, removes eye protection or stops working to take the time to remove and replace the dirty lens of the protective appliance.
Wilson et al. in U.S. Pat. No. 6,388,813 describe film construction that resolved many of these issues for lens systems. The construction is a multi-layer film construction of thin pressure sensitive adhesives interposed between clear polyethylene terephthalate sheets. The adhesive was coated, dried and laminated to the next adjacent sheet in the multi-layer stack eliminating air gaps that cause reflections and providing an appliance that had many sacrificial layers in the case of damage. The disadvantage of this construction is that there is no provision for an abrasion, scratch and chemical resistant surface; thus, the utility is limited to sectors of low use and abuse or disposable items.
Westfield et al. in U.S. Pat. No. 5,002,326 describe a windshield protector comprised of multiple layers of pressure sensitive adhesive coated polycarbonate film. The adhesive was coated, dried, and laminated to form a stack of protection film with a structure that allowed clean removal of the upper sheets and its associated adhesive from the next sheet in the multi-layer stack to reveal a clean fresh undamaged surface. The design and construction, as described, does not allow for cleaning or the incorporation of scratch and abrasion resistant properties.
While single layer security or anti-graffiti films do not suffer from the same time constraints for prompt removal, glass windows and the like suffer from their own unique set of problems, especially in the public transit sector. Although graffiti is a significant issue within the public transit industry; graffiti on metal, concrete or most surfaces can be washed away with cleaning solvents or simply painted over. Windows are different. Once windows in subways, buses and other areas of high use are scratched or damaged, either the window is left in service with the damage or the window must be replaced at high cost to the transit authority. Neither solution is very attractive—either the transit authority suffers damage to its reputation or it suffers high replacement costs. Single layer security films that are comprised of a single layer of adhesive coated chemical and abrasion resistant film are one of the solutions to the problem of scratching on glass; however, these films can be scratched as well and once they are, they must be replaced at relatively high removal and reinstallation costs.
Janssen et al. in U.S. Pat. No. 6,461,709 describe an article that includes a multi-layer chemical and abrasion resistant film to address the issues with single layer films, sacrificial plies and other solutions to graffiti in the transit market. The article consists of a UV curable abrasion and chemical resistant coating, which is cast onto the first side of a PET film from solvent, dried and cured with actinic radiation to produce a low surface energy abrasion and chemical resistant film. The '709 patent further describes coating from solvent of various pressure sensitive adhesive formulations onto the second side, which may have primer layers on it, of the same PET film, drying and laminating this adhesive coated side to the first side of a substantially identical film to create multi-layer stacks of abrasion, scratch and chemically resistant film with more than 1 removable layer.